Action: Automatically switch off wind turbines when bat activity is high

Key messages

Two studies evaluated the effects of automatically reducing turbine blade rotation when bat activity is high on bat populations. One study was in Germany, and one in the USA.

COMMUNITY RESPONSE (0 STUDIES)

POPULATION RESPONSE (2 STUDIES)

Survival (2 studies): Two replicated studies (one randomized, controlled and one paired sites study) in Germany and the USAfound that automatically reducing the rotation speed of wind turbine blades when bat activity is predicted to be high resulted in significantly fewer bat fatalities for all bat species combined and for little brown bats.

USAGE (0 STUDIES)

Background information and definitions

This intervention involves the use of automatic bat registration systems to monitor bat activity and shut down operation of wind turbines when bat activity reaches a predetermined ‘high’ level.

Supporting evidence from individual studies

1

A replicated, paired sites study in 2012 at eight pairs of wind turbines in Germany (Behr et al 2016) found that using automated ‘bat-friendly’ operating systems that reduced turbine blade rotation speed resulted in fewer bat fatalities than at normally operated wind turbines. Total bat fatalities and average collision rates were lower at automated turbines (total 21 bat fatalities, 0.06 fatalities/turbine/night) than at normally operated turbines (total 2 bat fatalities, 0.01 fatalities/turbine/night). At automated turbines, predictive models identified periods of high fatality risk and low energy yield from bat activity and wind speed data. During these periods, rotor blades were moved parallel to the wind to reduce rotation speed according to a target bat fatality rate (0.01 fatalities/turbine/night). Normally operated turbines rotated freely. At each of eight sites, automated and normal operating modes were alternated weekly between two paired turbines over 14 weeks in July–October 2012. Carcass searches were carried out daily. If applied to all turbines, it was estimated that automated operation would result in annual energy losses of 2.1%.

2

A randomized, replicated, controlled study in 2015 at a wind energy facility in Wisconsin, USA (Electric Power Research Institute 2017) found that using automated ‘Smart Curtailment’ operating systems that reduced turbine blade rotation speed resulted in significantly fewer fatalities for all bat species combined and for little brown bats Myotis lucifugus than at normally operated wind turbines. There was an 83% reduction in fatalities for all bats and a 90% reduction in fatalities for little brown bats at automated turbines (all bats: average 3 fatalities/day; little brown bats: 0.3 fatalities/day) compared with normally operated turbines (all bats: 18 fatalities/day; little brown bats: 3 fatalities/day). Twenty turbines were randomly selected for the study (10 operated by automated systems and 10 normally operated). At automated turbines, fatality risk was calculated by a predictive model using real-time bat activity and wind speed data every 10 minutes. If fatality risk was high (wind speed ≥3.5 m/s and >1 bat call detected in the previous 10 minutes), rotors were slowed (to ≤2 rpm) for 30 minutes. Normally operated turbines rotated freely. Carcass searches were carried out daily at all turbines in June–October 2015. Electricity generation was reduced by 90 MWh/turbine at automated turbines during the study period.

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Effectiveness

An assessment by independent experts of the effectiveness of this action based on the summarized evidence (0% = not effective, 100% = highly effective). This score is based on the direction and size of the effects reported in each study. Actions with high scores typically have large, desirable effects on the target species/habitat in each study. There is some variation between actions, e.g. 100% effectiveness in adding underpasses under roads for bat conservation will likely have different impacts to 100% effectiveness in restoring marsh habitat. The effectiveness score does not consider the quantity or quality of studies; a single, poorly designed study could generate a high effectiveness score. The effectiveness score is combined with the certainty and harms scores to determine the overall effectiveness category (for more details see https://www.conservationevidence.com/content/page/79).

Harms

An assessment by independent experts of the harms of this action to the target group of species/habitat, based on the summarized evidence (0% = none, 100% = major undesirable effects). Undesirable effects on other groups of species/habitats are not considered in this score. The harms score is combined with the effectiveness and certainty scores to determine the overall effectiveness category (for more details see https://www.conservationevidence.com/content/page/79).

Certainty

An assessment by independent experts of the certainty of the evidence for this action based on the summarized evidence (0% = no evidence, 100% = high quality evidence). How certain can we be that the effectiveness score applies to all targets of the intervention (e.g. all birds for an action in the bird synopsis)? This score is based on the number, quality and coverage (species, habitats, geographical locations) of studies. Actions with high scores are supported by lots of well-designed studies with a broad coverage relative to the scope of the intervention. However, the definition of "lots" and "well-designed" will vary between interventions and synopses depending on the breadth of the subject. The certainty score is combined with the effectiveness and harms scores to determine the overall effectiveness category (for more details see https://www.conservationevidence.com/content/page/79).

Overall Effectiveness Category

The overall effectiveness category is determined using effectiveness, certainty and harms scores generated by a structured assessment process with multiple rounds of anonymous scoring and commenting (a modified Delphi method). In this assessment, independent subject experts (listed for each synopsis) interpret the summarized evidence using standardised instructions. For more details see https://www.conservationevidence.com/content/page/79.